The present invention relates to a vehicle drive train unit and a vehicle drive system. The unit and system are particularly to suitable for an engine-motor hybrid vehicle, in which some wheels are driven by engine and others are driven by a motor.
A hybrid four-wheel drive train system with an engine and a motor for driving the vehicle has been known. In the system, either a front drive axle or a rear wheel drive axle (here, for example, a front wheel drive axle, hereinafter also called “front wheels”) is driven by an engine, while the other axle (for example, a rear drive axle, hereinafter also called “rear wheels”) is driven by motor as needed.
In the system, a four-wheel drive mode, in which both an engine and a motor operate, is used when a running load is large (for example, in starting a vehicle or in a climbing a gradient). On the other hand, a two-wheel drive mode in which only the engine is operated, is used during normal running when the load is relatively small (low load running range).
A hybrid four-wheel drive train system uses a DC motor or AC motor to drive wheels. Conventionally, apart from a power supply for accessories (for example, 12 V or 14 V alternator and battery for ordinary vehicle electric components), a generator for a wheel drive motor (for example, an alternator capable of generating power of 50 V or more) and a high-voltage battery for the motor have been used to power the motor (for example, Japanese Patent Laid-Open No. 2001-253256). A generator and a high-voltage battery are used because a 12 V or 14 V battery for accessories (ordinary electric components, such as starter, light, and air conditioner) and an alternator suited to such a battery cannot supply enough power to drive the wheel drive motor.
When wheels are motor-driven to start the vehicle, at the time of engine start when the engine speed is low and the output power of the wheel drive motor alternator is low, the alternator turns a separately-excited mode in which field current is supplied from the battery for accessories or the motor battery to the field coil of the alternator to increase the output power of the alternator. This output power is used to drive the motor. After the vehicle velocity reaches a predetermined level (for example 20 km/h), the alternator for the wheel drive motor generates enough power to drive the motor and uses its own output power to power the field coil (self-excited mode).
Japanese Patent Laid-Open No. 2000-224709 discloses a technique that a high-voltage generator and a main battery for a wheel drive motor and an auxiliary battery for accessories are provided to the vehicle. The high-voltage generator or the main battery is used to power the motor. Furthermore a DC-DC converter converts high-voltage power (for example, 250 V-350 V) from the generator into low-voltage power (12 V or 24 V) which is then supplied to the auxiliary battery
Japanese Patent Laid-Open No. 2001-63392 discloses a hybrid four-wheel drive train system that performs regenerative control by using a motor with a regenerative function (MG: motor-generator) as a means to drive, for example, rear wheels.
And when the vehicle is in braking, the motor (MG) functions as a generator for braking the vehicle, and regenerated energy from this MG is charged in a capacitor for the motor. The charged power in the capacitor is supplied to the MG so that the MG is used for auxiliary wheel drive control in starting or accelerating the vehicle on a normal or dry road surface of high coefficient of friction (high friction road).
Japanese Patent Laid-Open No. H5(1993)-219607 proposes the following drive train unit in an electric vehicle drive system. The unit comprises a translator, a motor and a differential gear where the translator and the motor are integrated into a unit, and the unit is directly attached to the differential gear which has a reduce function.